There are many applications for which controlling the environmental conditions within an enclosed space is important—for example, cooling data centers. A data center usually consists of computers and associated components operating 24 hours a day, 7 days a week. The electrical components in data centers produce a lot of heat, which needs to be removed from the space. Air-conditioning systems in data centers can consume as much as 40% of the total energy.
There are several methods to reduce the air-conditioning system's energy consumption in cooling only applications such as data centers, including, for example, conventional evaporative/adiabatic coolers, including indirect/hybrid designs for space cooling. Two general methods currently used are air-side economizers and water-side economizers. The air-side economizer runs outdoor air into the data center whenever outdoor air conditions are suitable to reject the heat from the data center. Using the air-side economizer can increase the risk of dust accumulation and air contaminants inside the space and may be limited to relatively cold and dry climates. The water-side economizer is usually a cooling tower which cools some or all of the return water in a chilled water loop. Water mineral deposition, micro-organisms and biofilm growth (e.g. Legionella bacteria), corrosion of metal components and other maintenance challenges in the tower are some of the drawbacks for the water-side economizer. Also, the water-side economizer application may be limited to relatively hot and dry climates.
Another recent cooling method is using direct evaporative coolers (DEC) to cool buildings and other enclosed spaces. Conventional direct evaporative coolers, although typically more energy efficient than vapor compression systems, have some drawbacks. The supply air temperature coming out of the cooler may be challenging to control and is dependent on the outdoor air temperature and humidity level. The supply air may be excessively humid. These systems need careful maintenance to ensure that bacteria, algae, fungi and other contaminants do not proliferate in the water system and transfer into the supply air stream. Since these systems utilize direct contact between the evaporating liquid water and supply air, carryover of contaminants into the air stream can occur, which can, in turn, lead to reduced indoor air quality, odors and “sick building syndrome.” Also, buildup of mineral deposits in the unit and on the evaporative pads can reduce performance and require maintenance.
In addition to maintenance challenges, direct and indirect evaporative coolers are typically limited to cooling temperatures no lower than the wet bulb temperature of the air stream travelling through the evaporative device. For example, if an indirect evaporative cooler uses outdoor scavenging air, the cooler may fail to meet the required cooling temperatures or handle the sensible load of a building space whenever the outside air wet bulb temperature becomes too high. This may limit the range of climate conditions suitable for the evaporative cooling technology, or necessitate the use of back up chillers whenever the evaporative system loses capacity. Redundant cooling equipment further increases the cost and complexity of the system.